Young cynomolgus monkeys Macaca fasicularus were inoculated intracerebrally with "Biken" strain of subacute sclerosing panencephalitis (SSPE) virus and monitored for clinical signs of disease. This is a long term project and signs of disease may not appear for 30 months, as was the case with one animal previously inoculated with the strain of SSPE virus. Attempts to rescue the "Delta Agent" from the dorsal root ganglion of experimentally infected patas monkeys Erythrocebus patas were unsuccessful. This part of the study will be terminated. Simian Hemorrhagic Fever (SHF) virus: A model for study of persistent infection. Four strains of SHF virus have been identified in patas monkey Erythrocebus patas. Two produce an acute infection in patas monkeys with the infected animal eliciting a high titer antibody response and complete recovery. The other two strains of SHF virus produce a persistent infection with low levels of circulating antibody.